Re: [uml-devel] [PATCH] fix extern inline errors with gcc 4.3.0

[David Shane Holden <dpejesh@yahoo.com>]

I tried to build a UML 2.6.26 kernel on Debian (32-bit) and ran into the 
same problem reported here http://marc.info/?t=121011533500002&r=1&w=2. 
  If I use gcc 4.3 everything works fine, but if I use gcc 4.1 or 4.2, 
UML crashes on startup.  I changed the gcc version check to 0430 and 
both 4.1 and 4.2 compiled kernels worked fine.

Also, is there any chance of getting a SKAS4 patch against 2.6.26?  I 
was trying to test it against 2.6.25.10 and had some strange issues.  I 
was running Debian Etch inside VMWare with a 2.6.25.10 SKAS4-enabled 
kernel.  When I tried to start up a UML instance from root or a non-root 
account I was getting the same problem reported here.. 
http://thread.gmane.org/gmane.linux.uml.user/13045/focus=13059.  Now the 
weird part is if I started UML via sudo from a non-root account I'd get 
a segfault somewhere in libc but then UML would boot up into a working 
Linux environment saying SKAS4 was enabled.  Was hoping to try and test 
it some more on a newer kernel if there's a patch available.

Benny Halevy wrote:
> gcc 4.3.0 needs -funit-at-a-time for extern inline functions
> otherwise it doesn't find their body.
> 
> For example:
> $ gcc --version
> gcc (GCC) 4.3.0 20080428 (Red Hat 4.3.0-8)
> 
> /usr0/export/dev/bhalevy/git/linux-pnfs-bh-nfs41/fs/buffer.c: In function ‘alloc_page_buffers’:
> /usr0/export/dev/bhalevy/git/linux-pnfs-bh-nfs41/fs/buffer.c:51: sorry, unimplemented: inlining failed in call to ‘init_buffer’: function body not available
> /usr0/export/dev/bhalevy/git/linux-pnfs-bh-nfs41/fs/buffer.c:948: sorry, unimplemented: called from here
> 
> Fix follows the lines of commit 22eecde2f9034764a3fd095eecfa3adfb8ec9a98
> that was reverted by commit c0a18111e571138747a98af18b3a2124df56a0d1,
> just limiting the flag for pre- gcc 4.3.0 rather than 4.0.
> 
> Signed-off-by: Benny Halevy <bhalevy@panasas.com>
> ---
>  arch/um/Makefile |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/um/Makefile b/arch/um/Makefile
> index dbeab15..e7ed37b 100644
> --- a/arch/um/Makefile
> +++ b/arch/um/Makefile
> @@ -77,7 +77,11 @@ include $(srctree)/$(ARCH_DIR)/Makefile-os-$(OS)
>  KERNEL_DEFINES = $(strip -Derrno=kernel_errno -Dsigprocmask=kernel_sigprocmask \
>  			 -Dmktime=kernel_mktime $(ARCH_KERNEL_DEFINES))
>  KBUILD_CFLAGS += $(KERNEL_DEFINES)
> -KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time,)
> +# Disable unit-at-a-time mode on pre-gcc-4.3 compilers, it makes gcc use
> +# a lot more stack due to the lack of sharing of stacklots:
> +# gcc 4.3.0 needs -funit-at-a-time for extern inline functions
> +KBUILD_CFLAGS += $(shell if [ $(call cc-version) -lt 0403 ] ; then \
> +			echo $(call cc-option,-fno-unit-at-a-time); fi ;)
>  
>  PHONY += linux
>  


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